1. Field of the Invention
This invention relates to a projector for use in a planetarium and, more particularly, to an invention effective in an auxiliary projector other than a fixed star projector and a planet projector.
2. DescripIon of Related Art
In a planetarium, as well as projectors for projecting star bodies such as a fixed star projector and a planet projector, a variety of auxiliary projectors are used to enhance stage effects. Such projectors achieving widespread use include a so-called slide projector in which an illuminating light emitted from a light source 21 passes through a condenser lens 22, then through an original projection plate 23 on which a light-permeable pattern P is formed, and then through a projection lens 24 to project the transmitted image onto a dome screen S (see FIG. 9). An electric lamp is employed as the light source in such projector. Light emitted from the electric lamp is reflected by a reflecting mirror 25. The reflected light is also gathered by the condenser lens 22 and passed through the original projection plate 23.
Some images to be projected by the auxiliary projector in this manner are formed by the light-permeable pattern extending across the entire original projection plate, but in other case the light-permeable pattern has an area occupying only part of the entire projection plate, for example, a picture pattern such as a constellation and a space ship, and a coordinate system pattern such as the equator. For example, FIG. 10 shows a original projection plate 23 having a light-permeable pattern P for the equator, in which an area P1 of the light-permeable pattern is only the area surrounded by the long-dashed short-dashed line. However, in a projector in the prior art employing an electric lamp as a single light source, after the light emitted from the light source has been conically diffused, the diffused light is conically gathered by the condenser lens 22, and then passed through the original projection plate 23. Accordingly, a non-light-permeable portion B positioned around the area P1 of the light-permeable pattern is also uselessly irradiated with the light.
Due to the consumption of electric power for such wasted irradiation, the projector in the prior art is uneconomic as well as producing additional heat. As a result, there are problems of an increase in size of the projector, and of the unavoidable use of a glass-made original plate with high cost and low operability without general versatility because the high temperature inside the projector does not permit the use of a film-type original plate of low heat resistance as the project original plate.
It is therefore an object of the present invention to solve the problems associated with the prior art as described above, and to provide a projector having new advantages. The present invention disclosed herein essentially has three features. According to a first of the three features, the present invention provides a projector for irradiating an original projection plate provided with a light-permeable pattern with an illuminating light to project a transmitted image through a projection lens onto a dome screen, which comprises a light source including an array of a plurality of light emitting diodes for emitting the illumination light.
According to a second feature, based on the first feature, the light emitting diodes are arranged in a configuration allowing an area of emission of the illuminating light onto the original projection plate to be minimized to a region covering a light-permeable area of the light-permeable pattern.
According to a third feature, based on the first feature, when a projected image straddles a horizon on the dome screen, part of the array of light emitting diodes are shut off to block projection below the horizon.
The present invention effectively provides unique advantages as follows.
(1) In consequence of using light emitting diodes as the light source, the electrical power consumption is reduced as compared with the use of an electric lamp. Particularly, when the light emitting diodes are arranged in a configuration allowing an area of emission of the illuminating light onto the original projection plate to be minimized to a region covering a light-permeable area of the light-permeable pattern, the electrical power consumption is further reduced.
(2) Likewise, the amount of heating in the projector according to the present invention is lower than that in the conventional projector using an electric lamp. Accordingly, it is possible to use a film-type original plate, especially, a color film-type original plate as the original projection plate, which is difficult in the prior art, resulting in advantages in cost, productivity and general versatility.
(3) A flat plate-shaped Fresnel lens is employed for a condenser lens. Therefore the use of such condenser lens, together with a light source with the small thickness, makes it possible to decrease the length of the projector. At the same time, the setting of the arrangement of the light emitting diodes as described in advantage (1), and further the setting the condenser lens having a shape to fit the light-permeable pattern, allow reduction of the projector in width and vertical dimensions. Since there is no worry of the occurrence of internal overheating even in the event of a decrease in size due to the low amount of heating as described above, a significant reduction in the overall size of the projector is achieved.
(4) A combination of the light emitting diodes with different colors used as the light source facilitates the color-coding of the projected images. Hence, it is possible to overcome the problem associated with constraints on the projection of color images due to the fact that the heat causes a fading of the color in the colored original projection plate.